Phytopathogenic bacteria such as Pseudomonas syringae pv. tomato deliver effector proteins to plant cells in order to modify the activities of the host to favor bacterial colonization. Plants produce specific immune receptors (R proteins) that recognize the presence of bacterial effectors and subsequently initiate plant disease resistance responses. An emerging paradigm in plant resistance to bacteria is that R proteins recognize modulation of host proteins by effectors and initiate resistance responses following perturbation of these host targets. A putative virulence target of the P. syringae effector AvrRpt2 has been identified. Expression of AvrRpt2, a cysteine protease, in Arabidopsis plants results in the degradation of host RIN4 protein. Degradation of RIN4 correlates with initiation of resistance responses elicited by AvrRpt2. The purpose of the proposed research is to determine whether AvrRpt2 directly degrades RIN4, to identify proteins associated with RIN4 and to establish how AvrRpt2-mediated degradation of RIN4 triggers resistance. [unreadable] [unreadable]